This invention relates to the use of compounds containing amide or imide type functional groups to increase the rate and/or selectivity of the nitroxide mediated oxidation of alcohols, particularly the primary alcohol groups on cellulose, cellulose pulp or cellulose fiber. Aldehyde modified cellulose, cellulose pulp or cellulose fiber prepared by such oxidation is particularly useful in making paper.
The term xe2x80x9cpaperxe2x80x9d as used herein, includes sheet-like masses and molded products made from cellulose, cellulose pulp or cellulose fiber material that may be derived from natural sources. Paper may also be made from synthetic cellulosic fibers and regenerated cellulose as well as recycled waste paper. In addition, paper made from combinations of cellulosic and synthetic materials are applicable herein. Paperboard is included within the broad term xe2x80x9cpaperxe2x80x9d.
Papermaking, as it is conventionally known, is the process of introducing an aqueous slurry of pulp or wood cellulosic fibers, which have been beaten or refined to achieve a level of fiber hydration and to which a variety of functional additives can be added, onto a screen or similar device in such a manner that water is removed, thereby forming a sheet of the consolidated fibers, which upon pressing and drying can be processed into dry roll or sheet form. Typically in papermaking, the feed or inlet to a papermaking machine is an aqueous slurry or water suspension of pulp fibers which is provided from what is called the xe2x80x9cwet endxe2x80x9d system. In the wet end, the pulp along with other additives are mixed in an aqueous slurry and subjected to mechanical and other operations such as beating and refining. Various additives are commonly added to help provide different properties in the paper product.
The preparation of aldehyde containing starches and the use of such aldehyde derivatives in the paper industry as wet and dry strength additives is well known. Both oxidative and non-oxidative methods are known for introducing aldehyde groups into starch. Use of these products in papermaking to provide wet and dry strength properties involves the addition of this separate starch additive component.
The use of nitroxyl radicals and nitrosonium salts in organic chemistry as an oxidative route to produce aldehydes and carboxylic acids from primary and secondary alcohols is disclosed in an article entitled xe2x80x9cOrganic Nitrosonium Salts As Oxidants in Organic Chemistryxe2x80x9d by J. M. Bobbitt and C. L. Flores, in Heterocycles, Vol. 27, No. 2, 1988, pp. 509-533. Recently, application of this chemistry was extended to the selective oxidation of primary alcohols in various carbohydrates to carboxylic acids in an article entitled xe2x80x9cSelective Oxidation of Primary Alcohols Mediated by Nitroxyl Radical in Aqueous Solution. Kinetics and Mechanismxe2x80x9d by A. E. J. de Nooy and A. C. Bessemer, in Tetrahedron, Vol. 51, No. 29, 1995, pp. 8023-8032. Patent publication WO 95/07303 dated Mar. 16, 1995 further discloses the use of this technology in which carbohydrates having a primary hydroxyl group are oxidized under aqueous conditions to form products having a high content of greater than 90% carboxyl groups. This art involving the oxidation of primary alcohols generally describes the preparation of polyglucuronic acids with high carboxylic acid content. Similarly, the process of oxidation has been used to prepare various polysaccharides with high carboxyl content as described in xe2x80x9cOxidation of Primary Alcohol Groups of Naturally Occurring Polysaccharides with 2,2,6,6-Tetramethyl-1-piperidine Oxoammonium Ionxe2x80x9d by P. S. Chang and J. F. Robyt in J. Carbohydrate Chemistry, 15(7), 1996, pp. 819-830. It should be noted that in some applications high carboxylic acid content is undesirable.
Recent patent publications WO 99/23240 and 99/23117, both dated May 14, 1999, respectively disclose methods of oxidizing starch and cellulose using an oxoammonium ion producing reagent in the presence of an enzyme oxidizing agent.
It has recently been discovered that use of selective oxidation with a limited amount of oxidant and a nitroxyl radical mediator under defined reaction conditions provide oxidized cellulose material with effective aldehyde content. Aldehyde modified pulp prepared in this manner contains from 1 to 20 mmoles of aldehyde and 1 to 40 mmole carboxylic acid per 100 grams of cellulose. Such aldehyde modified pulp is used in the production of tissue/towel and other paper products which exhibit unexpected high wet strength, temporary wet strength and dry strength properties and high wet strength/dry strength ratios without the use of other additives.
It would be commercially desirable to improve the rate of nitroxide mediated oxidation of cellulose pulp as slow oxidation rates are disruptive to traditional manufacturing of papermaking and may result in degradation of the cellulose. Surprisingly, it has now been discovered that the use of compounds containing amide or imide type functional groups increases the rate of nitroxide mediated oxidation of alcohols. In particular, such amide or imide compounds increase the rate of nitroxide mediated oxidation of cellulose, cellulose pulp or cellulose fiber, such that it is commercially compatible with the traditional paper making process. In addition, the increased rate of nitroxide mediated oxidation may effectively reduce the occurrence of degradative side reactions. Such co-catalysts may be used to increase the absolute amount of aldehyde groups on cellulose, cellulose pulp or cellulose fiber, thereby further increasing the inherent wet strength, temporary wet strength, and dry strength of paper made with such cellulose, cellulose pulp or cellulose fiber.
This invention pertains to the use of compounds containing amide or imide type functional groups to increase the rate of nitroxide mediated oxidation of alcohols. While suitable for oxidation of alcohol groups on a variety of substrates, it is particularly useful to oxidize cellulose, cellulose pulp or cellulose fiber so that it is commercially compatible with the traditional paper making process. Such co-catalysts may be used to increase the absolute amount of aldehyde groups on cellulose, cellulose pulp or cellulose fiber, thereby further increasing the inherent wet strength, temporary wet strength, and dry strength of paper made with such cellulose, cellulose pulp or cellulose fiber.
More particularly, this invention pertains to using poly(acrylamide) homo- and/or co-polymers of various compositions and molecular weights to increase the rate of nitroxide mediated oxidation by at least two-fold and to increase the absolute amount of aldehyde groups by up to at least 5%.
This invention further involves the method of preparing paper having wet strength, temporary wet strength and dry strength properties comprising using the cellulose aldehyde pulp prepared by the selective oxidation procedure as described above, as the paper or pulp stock or a component thereof and the resultant paper.